Re: [PATCH net-next v3 4/9] gve: Add support for dma_mask register

[Jakub Kicinski]

On Tue,  8 Sep 2020 11:39:04 -0700 David Awogbemila wrote:
> +     dma_mask = readb(&reg_bar->dma_mask);
> +     // Default to 64 if the register isn't set
> +     if (!dma_mask)
> +             dma_mask = 64;
>       gve_write_version(&reg_bar->driver_version);
>       /* Get max queues to alloc etherdev */
>       max_rx_queues = ioread32be(&reg_bar->max_tx_queues);
>       max_tx_queues = ioread32be(&reg_bar->max_rx_queues);
> +
> +     err = pci_set_dma_mask(pdev, DMA_BIT_MASK(64));

You use the constant 64, not dma_mask?

You jump through hoops to get GFP_DMA allocations yet you don't set the
right DMA mask. Why would swiotlb become an issue to you if there never
was any reasonable mask set?

> +     if (err) {
> +             dev_err(&pdev->dev, "Failed to set dma mask: err=%d\n", err);
> +             goto abort_with_reg_bar;
> +     }
> +
> +     err = pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(64));

dma_set_mask_and_coherent()

> +     if (err) {
> +             dev_err(&pdev->dev,
> +                     "Failed to set consistent dma mask: err=%d\n", err);
> +             goto abort_with_reg_bar;
> +     }